This invention relates generally to improvements in automatic, bladder-type, tire shaping and curing presses and peripheral equipment therefor, and more particularly to a bladder leak and rupture detector utilized in such presses for detecting the presence of bladder failures.
In the conventional practice of shaping and curing tires in tire curing presses, an uncured tire carcass is placed between a heated stationary lower mold section, a heated movable upper mold section, and a heated, fluid inflatable, shaping bladder which is disposed within the tire carcass. With the tire carcass in position, the press automatically and concurrently lowers the upper mold section and introduces cure media under pressure into the bladder to shape the tire carcass firmly against the mold sections, thereby both shaping and vulcanizing the tire. The tire carcass is retained in the heated mold section for the requisite time period necessary to achieve vulcanization and, upon completion of the vulcanization period, the fluid pressure is reduced and cure media removed during "blow-down" from the bladder interior, the bladder then is stripped from the cured tire and the upper mold section is raised to allow removal of the tire.
Operating in conjunction with presses of the foregoing type, tire loaders, unloaders, post-cure inflators and conveyors are employed automatically to transport the tire carcasses to the presses, locate the carcasses on the presses, remove the cured tires after cycling of the presses, post-cure inflate the tires and transport the tires to an inspection station. Thus, from the time the green tires are placed at the point where they are picked up for subsequent curing in the press, until the shaped and vulcanized tires are inspected at the inspection station, the processing of the tires is almost completely automatic. Should a malfunction occur which allows defective tires to be produced, a number of imperfect tires may be turned out by the curing press before the defect can be discovered and traced back to the press which is responsible.
One of the major malfunctions in curing presses to which "cure defects" are attributable is a ruptured or leaking bladder. The defects associated with such bladder failures result often in one of two ways. Because of leakage of the cure media through the bladder, the press is unable to develop sufficient pressure within the bladder to properly shape the tire. Alternatively, the deflect in the bladder allows the cure media to penetrate the ply fabric of the tire, which, in turn, usually results in a scrap tire because of ply separation within the tire.
Rupture of the bladder normally results when the bladder is worn out. Such rupture is usually visually perceptible by the operator who would then shut down the machine and replace the bladder. The tire in the press at the time of rupture would necessarily be defective and scrapped. Although the operator would normally visually perceive the rupture, it is desirable nonetheless to provide a detector to prevent automatically loading of new tires in the event of the bladder rupture. Moreover, it is desirable automatically to shut off the curing fluid to the press in the event of the bladder rupture.
The more difficult malfunction to detect is the leaky bladder where leakage is at a rate significantly less than the massive leaks that occur when the bladder ruptures. Often such lesser leaks prelude the rupture of the bladder and quick detection could reduce the occurrence of bladder ruptures. In normal operation, such lesser leaks are not always promptly noted or detected by even careful press operators. Should a malfunction of this type occur, a large number of defective tires may be cured prior to detection of the same.
In known detection systems of the type which monitor for such leaks and ruptures of the bladder, several basic problem areas exist. Conventional detection systems oftentimes employ static pressure responsive switches which utilize rubber diaphragms. During use, the rubber diaphragms age and harden resulting in a change in the pressure level actuating the switch. Accordingly, such type of switches have relatively poor repeatability and when hardened sufficiently, are subject to failure. Moreover, in such systems, the pressure switch settings are very critical and unstable. Many false failure signals may result from a low setting and the system arrangement of the pressure switches, particularly during shaping. Often, the press operator is faced with either setting the pressure switches at low setting to ensure detection of leaks at the cost of increased false failure signals. Alternatively, the operator could employ a high setting; however, such may result in some leaks going undetected leading to defective tires.
Another problem area in known detection systems is that only one portion of the mold cavity is monitored for leaks. Accordingly, a small leak may exist within the unmonitored portion of the mold cavity which is of insufficient pressure to migrate to the detection device. Accordingly, the bladder defect may go undetected.